The present invention relates to an apparatus for inspecting the light-emitting state of an RGB (red, green, blue) phosphor screen of a face plate of a color CRT (cathode ray tube).
FIG. 3 shows a generally know color CRT. In the figure, a reference numeral 1 depicts a color CRT. The color CRT is formed by an electron gun section 6 and a face plate 7. In the electron gun section 6, a tube 2 made of lead glass, barium glass or the like, contains three (or one) electronic guns 3, a focusing electrode 4, a convergence electrode 5 or the like. The face plate 7 is combined with the entirely opened side of the electron gun section 6 by means of a welding process or the like thereby to form an airtight vacuum space together with the tube 2. As the same as the tube 2, the face plate 7 is made of lead glass, barium glass or the like. The face plate is formed by a front glass plane 8, an RGB phosphor screen 9 on which phosphor dots of R, G, B are disposed in a mosaic fashion, and a shadow mask 10 or the like. A metal back layer 11 formed by an aluminum film with a thickness in a range of about 5xc3x9710xe2x88x924 to 5xc3x9710xe2x88x926 cm, for example, is formed at the rear surface side of the RGB phosphor screen 9. In FIG. 3, reference numerals 12 and 13 depict deflection yoke and a color purity adjusting coil disposed in the vicinity of the outer portion of the tube 2.
The face plate 7 of the aforesaid color CRT 1 may be damaged during the manufacturing process thereof in such a manner that the aluminum enters into the RGB phosphor screen 9. Thus, it is required to inspect the face plate. However, conventionally, as shown in FIG. 4, the face plate is inspected in a state where the face plate 7 is combined with the electron gun section 6 and so the face plate is incorporated within the color CRT 1 operable as a completed color CRT.
To be more concrete, as shown in FIG. 4, the face plate 7 is combined with the electron gun section 6 and the inner portion thereof is placed in a vacuum state thereby to complete the color CRT 1, then suitable driving voltages are supplied to the respective portions of the electron gun section 6, and the light emitting sate of the R, G, B phosphor dots on the RGB phosphor screen 9 at the time where an electron beam 14 is irradiated on the RGB phosphor screen 9 is observed by a color CCD (charge-coupled device) camera 15. The output of the color CCD camera 15 is subjected to the image processing by a computer 16 having an image processing function to inspect whether or not there is a defect on the RGB phosphor screen 9. In FIG. 4, a reference numeral 17 depicts a corn-shaped hood for shielding the external light from being incident therein.
However, according to the aforesaid conventional method of inspecting the face plate for the color CRT, the inspection is not performed as to the face plate 7 itself in a state separated from other parts but the inspection is performed in a state where the face plate is incorporated within the completed color CRT 1. Thus, at the time of the inspection, it is required to perform the operations for combining the electron gun section 6 with the face plate 7 and for exhausting air within the tube so as to place the inner portion thereof in a vacuum state after the combining operation. Further, when it is determined that there is a damage at the face plate 7 as the result of the inspection, it is required to detach the face plate 7 from the electron gun section 6 and, at the time of the detaching, the electron gun section 6 having no defect portion may be damaged. In this manner, there arise problems that the inspection efficiency and the productivity are not good.
The present invention has been attained in view of the aforesaid conventional problems.
An object of the present invention is to provide an apparatus for inspecting a face plate for a color CRT (hereinafter referred to inspection apparatus for a face plate) which can efficiently inspect the face plate itself in a state separated from other parts without joining the face plate with an electron gun section.
In order to attain the aforesaid object, an apparatus for inspecting a face plate for a color CRT according to the present invention includes: a soft X-ray source for generating a soft X-ray; a vacuum box disposed in front of the soft X-ray source and having a pair of soft X-ray windows for passing the soft X-ray generated by the soft X-ray source therethrough; the face plate for the color CRT disposed at a rear side of the vacuum box; a color camera for observing a light emitting sate of an RGB phosphor screen of the face plate for the color CRT at a time where the soft X-ray generated from the soft X-ray source is irradiated on the face plate for the color CRT through the vacuum box; and an image processing unit for analyzing a color picture obtained from the color camera.
In the inspection apparatus for a face plate according to the present invention, the inspection of the face plate can be performed by using only the face plate itself in a state separated from other parts without combining the face plate to be inspected with the electron gun section. Thus, unlike the conventional inspection method, since the present invention does not require the combining procedure nor the exhausting and vacuum forming procedure for each face plate, the inspection efficiency can be improved and the productivity of color CRTs can also be improved.